Vibration-isolated self-leveling platform and method

ABSTRACT

A pneumatically supported, load-carrying platform that is precisely controlled against minute excursions from a predetermined position while being cushioned against shock and vibration. The platform structure preferably is pendulously supported by a group of spaced pneumatically pressurized mounts or air springs, having individual sensors responsive to incipient deviations in the platform position and which control the pressure applied to the respective mounts so as to restore or maintain the platform within normal limits. Sensitivity of response, and adjustment of the system stability results from regulating the supply of air available to the mounts, and furnishing preestablished incremental pressures above the pressures needed for proper operation of the mounts, which incremental pressures are substantially independent of both the mount pressure and the pressure from the source of supply.

United States Patent [72] Inventors Norman C. Pickering Sag Harbor,N.Y.; Joseph P. Roberts, Arleta, Calif. [21] Appl. No. 833,570 [22]Filed June 16, 1969 [45] Patented May 1l, 1971 [73] Assignee ROBINTECHIncorporated [54] VIBRATION-ISOLATED SELF-LEVELING PLATFORM AND METHOD19 Clalms,' 4 Drawing Figs.

[52] U.S. Cl 248/20, 10S/136, 24S/188.3 [5l] Int. Cl A47b 9/02 [50]Field of Search 248/20, 22, 23, 19,13, 188.3;280/6,6.1,6.ll; 180/41;137/596, 627.5; 108/136 [56] References Cited UNITED STATES PATENTS2,173,342 9/ 1939 Rosenzweg 248/20 2,605,066 7/ 1952 Brown 248/202,706,607 4/ 1955 Withers et al 248/22 FOREIGN PATENTS 1,064,671 4/1967Great Britain Primary Examiner-Roy D. Frazier Assistant Examiner-JFranklin Foss Attorney-Wilbur J. Kupfrian ABSTRACT: A pneumaticallysupported, load-carrying plat- Sensitivity of response, and adjustmentof the system stability results from regulating the supply of airavailable to the mounts, and furnishing preestablished incrementalpressures above the pressures needed for proper operation of the mounts,which incremental pressures are substantially independent of both themount pressure and the pressure from the source of supply.

PatentemMay 11', 1971 f 3,573,278

2 Sheets-Sheet l 3| i I3 'I 22 l0 l 24 l 56 2s il iy I INVENTORS NORMANC. PICKERING 4| JosEPHHRoBERTs I .Y l- Y VIBRA'IION-ISOLATEI)SELF-LEVEL'ING PLATFORM y AND METHOD lBACKGROUND OF THE INVENTION tion,and inspection devices, so they are isolatednot only from distortions inthe framework of the equipment resulting from settling in the floor orfoundation, but also as a safeguard 'against the undesirable effects ofshock and vibration resulting from outside influences. The invention hasapplication also where it is desired to maintain a stable referenceplane with v respect to a movable device, or while a device is intransit, to

free it of the disturbing influences introduced, for example, by themotion of the vehicle. Also in the case of miniaturizedintegrated-circuitry, certain equipment needed for'producing orinspecting minute parts often is rendered inoperable or ineffective byinfluences such as vibration created by heavy machinery operating in thevicinity, or 4by the passage of vehicular trafc in the'neighboringstreets, even though the equipment is finnly .anchored in the ground,and even when the anchoring means is isolated from the foundation of thebuilding in which the equipment is located.

It has been customary in recent years to support delicate equipment onsuch aselectro-optical devices, inertial platform checkout systems,laser welders, comparators and the like, on active vibration isolators,such as servo-controlled pneumatic means, that also maintains theequipment within prescribed limits of deviation from an establishednorm. Typically the supporting structure comprises a table having arelatively massive platform that may be maintained in a level position,through the use of pneumatic supporting `media responsive to incipientdeviations in the position of the platform from the normal levelposition.

While devices of this sort utilizing conventional servosystem conceptshave functioned reasonably well, a continuing demand has been indicatedfor equipment; that exhibits more complete control of the dynamicresponse, that yet is capable of providing greater system sensitivitywith reasonable response time, and stiffer responses to rapidly changingloads with reasonable freedom from overtravel and oscillation thatnormally is associatedlwith transient disturbances. There is acontinuing need also for a corrective action that is somehow related tothe degree of disturbance, so that unusually large deviations triggercorrespondingly great'and rapid restoring actions.

It is accordingly an object of the present invention to provide animproved method of an apparatus for stabilizing a load-bearing platfonnincorporating new land useful concepts for obtaining increasedsensitivity and improved dynamic control of an active servosystem formaintairiing such a platform in stable condition.

SUMMARY oF INVENTION This invention utilizes a number of design conceptsthat contribute to an improved structure offering advantages over theinvention may be applied to stabilized lstructures generally, forpurposes of illustration the invention is illustrated as applied to aself-leveling table, herein shown as a surface plate which may be ofconventional design, normally being formed of granite orcast-ferrousmetal. This pla'te and a supporting framework together'formthe platform which is to be stabiltively thick surface plate; hence bysupporting the platform at points near its upper extremity, a pendulousstructure results with an inherently greater natural stability, whichimparts additional stability to the system, as compared with thosestructures that-are supported beneath theplatform.

The supports for the platform may comprise conventional pneumaticmounts, sometimes called air springs, that functionally comprisepressurized chambers, each having a movable piston or diaphragm on whicha portion of the platform rests, the piston or diaphragm being urgedupwardly in response to the pressure within the chamber. As many ofthese air mounts or springs are used as are necessary for propersupvporting action, though in a preferred form of the invention four areemployed, with the points of support being located at the comers of theillustrated rectangular platform. A group of sensing devices locatedclose to the air mounts d etect incipient deviations in the position ofthe respective portions of the platform with which each of the devicesis associated, and the sensing devices control the flow of pneumaticfluid to the supporting mounts at a time and in a manner effective torestore the vindividually supported portions to their normal positions.Special valve design provisions regulate the flow of air or otherpneumatic fluid with the help of pressure-regulating means employed tomaintain an input pressure that represents a constant increment over thenormal pressure required for proper functioning of the air mounts.Additional features of the invention include a mechanism for throttlingand diverting portions of the flow of fluid from the source to a dampingchamber, to selectively modify. the response of the air mount. The valvemechanism is designed also to compensate for unusual excursions in theplatform position so as to provide a more rapid and a more effectivecorrective action in the air pressure when such unusual circumstancesarise.

BRIEF DESCRIPTION OF THE DRAWINGS While the scope of the invention iscomprehended by the llanguage of the claims which are appended to thefollowing specification, and which distinctly point out and claim thesubject matter of the invention, it is .believed that a betterunderstanding of the inventive concepts may result by reference to theaccompanying drawings, illustrating some specific emlwhat has been knownheretofore. Although the principles of bodiments, and in which:

FIG. l is a modified perspective view of a table structure adapted tosupport a surface plate, with certain portions of the framework andhousing being broken away to illustrate features of the invention; FIG.2 is a vertical sectional view of a slightly variant form of air mountand'its relationship to one of the tubular table legs, with certainparts being shown in elevation;

FIG. 3 is a vertical sectional view taken generally along the line 3-3of FIG. l to show the generally pendulous nature of the platformsupport; and

FIG. 4 is a vertical cross-sectional view of an enlarged embodiment ofan air control valve, with vrelated sensing and pressure-regulatingmechanisms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring again to the drawingsand more particularly to FIG. 1 thereof, the device comprises a tablel0, preferably y I having a plurality of tubular supporting legs 1l andsuitable reinforcing structural members 12. A sheet metal skirt 13 maytremity, and from which the platform preferably is supported. v l

A plurality of lateral members 16 secured to the platform 14 near thelower extremity serve as a support for a suitable working surfaceprovided as shown in FIGS. 1 and 3 by a relatively massive surface plate17, illustrated in FIG. 1in phantorn lines. The upper exposed surface 18of the plate 17 constitutes a relatively precisely formed plane that isto be maintained in a stable state, and which provides a support for atool, a measuring instrument or the like 19, also illustrated in FIG. lin phantom lines.

The platform 14 is supported at several spaced points, as previouslyindicated, to provide the maximum degree of equilibrium. A pneumaticallycushioned air mount or spring 21 is interposed at the top of each legl1, or at such other points of the table as will provide stable supportfor the platform. In the embodiment shown, the mounts 2l located at thetop of the legs 11, support the platform 14 pendulously, as best seen inFIG. 3. With the arrangement illustrated, the platform accordingly hasfour major points of support, two of which may operate in tandem, aswill appear, to provide the stability normally associated with athree-point support. Optionally two of the supports shown at one end ofthe table and functioning in tandem might be replaced by a singlecentrally positioned unit to provide three-point support. ln a typicalapplication, a surface plate may measure 24 inches by 36 inches andweigh 250 pounds. A resulting stabilizing pendulous moment of 250 poundsinches is created when the points of support are located l inch abovethe center of gravity of the combined platform mass.

The air spring 2l may be of any conventional design and is illustratedin FIG. 2 as comprising a pressurized chamber 22 formed of a base plate23, tubular sidewalls 24, and a flexible diaphragm 25 that flexes in themanner of a bellows. The diaphragm 25 preferablyl is made of suitableelastomeric material, or an elastomerically coated polyester resin ornylon fabric that is capable of forming with the base and sidewalls afluidtight chamber. A plunger 26 having a cover plate 27 is partiallyenclosed by a lower cup-shaped portion of the diaphragm 25, and ismovable in a vertical direction as the diaphragm flexes in response tofluid pressure within the chamber 22.

A suitable arrangement may be provided for securing the diaphragm 25relative to the plunger 26, and for herrnetcally sealing the diaphragmrelative to the housing of the air mount 21. For example, the diaphragmmay be cemented to the bottom of the plunger 26, or a clamping plate 31with suitable fasteners may be utilized. As best seen in FIG. 2 thediaphragm has a radial flanged portion 32 which may be sealed between aclamping ring 33 and a flange 34 projecting from ther-tubular sidewalls24, as by capscrews 35. The air spring is rendered functional by theadmission of pressurized pneumatic fluid through a tube 36, and inletconnection 37 communicating with an air control valve as will appear.

The plunger 26 is shown in an equilibrium position, wherein the pressurewithin the chamber 22 applied to the diaphragm balances the weightapplied to the plunger 26. A threaded cavity 38 may receive a threadedstud 39 by which the weight of the platform 14 and load 19 may betransmitted from the flange to the plunger 26. It will be observed thatthe plunger 26 floats within its supporting enclosure, and has limitedfreedom in both horizontal and vertical directions. A certain amount oflateral damping may be introduced by controlling the dimensions of thediaphragm 25. It will be observed in FIG. 2 that a smaller diameterportion of the diaphragm extends upwardly about the plunger or piston26, while a depending larger diameter portion 28 is joined to it by ashifting intermediate section 29. In cross section the flexing reentrantpart of the diaphragm resembles a hairpin, the length of whichdetermines the degree of diaphragm motion, while inversely contributingto lateral damping; the shorter the reentrant loop, the greater thedamping factor.

A portion of the air flowing through inlet connection 37 may be divertedfrom the pressurized chamber 22 by means of a controlled bypass 41, theamount of diverted flow being regulated in part by a needle valve orthrottle 42, consisting essentially of an adjustable orifice. ln thismanner, a predetermined amount of the pneumatic fluid may be caused toflow into one of the tubular legs l1, which being sealed at both top andbottom forms a damping chamber 43. The plunger 26 is responsive to thepressure within the chamber 22, which is affected by the amount of inletair being diverted through tube 41, which in part is determined also bythe pressure within the chamber 43. Accordingly the response of theplunger 26 may be controlled in great measure by the setting of theneedle valve 42 and the stabilizing effect of the damping chamber 43. Ina typical installation the volumetric capacity of the damping chambershould be a multiple of and preferably at least three times thevolumetric capacity of the pressurized work chamber 22. Also, in atypical system the natural response frequency might vary through a rangeof from 0.6 Hz. to 2.0 l-Iz., the frequency being regulated in largemeasure by the valve 42 opening. Opening the valve tends to bypassA moreof the fluid to the chamber 43, decreases the natui'al' frequency andincreases the response time, producing a softer correction, whileclosing the valve 42 increases the natural frequency and the stiffnessof the system.

In accordance with the laws of physics, the force exerted upwardly oneach plunger 26 is the product of the effective area of the diaphragm 25and the pressure within the chamber 22. In a typical installation theeffective area of one of the air springs 21 may be of the order of 7.5square inches. Assuming pressure within the chamber of p.s.i., thetheoretical maximum upward thrust would be 600 pounds, or if four suchmounts were provided per installation, the total capacity of such atable would be 2,400 pounds. If the dead load weight of the platformwere 400 pounds, the useful capacity of such a table for live loadswould be 2,000 pounds.

As indicated earlier, the air spring 21 is actuated in response to acontrol valve of improved design. Referring again to the drawings, andmore particularly to FIGS. 1, 3 and 4, such a valve 44 includes a valvebody 46 having an inlet port 45, illustrated as a standard threadedopening for receiving pipe or tubing that may be connected with asuitable source of compressed pneumatic fluid, not illustrated.Customarily, well-filtered dry air of the type available in mostindustrial shops, and under a suitable pressure commonly around p.s.i.is most economical for the purpose, though the relatively low fluidconsumption of the present system often justifies the use of bottledgas, such as nitrogen, particularly for mobile applications. Thepressure, whether regulated from cylinders, or from a pressure-regulatedcompressor and storage system, primarily determines the load-supportingcapability of the self-leveling platform. ln any case it must beadequate so that a predetermined somewhat lower pressure availablewithin the work chamber 22 exerts the required lifting effort on thepiston 26.

As best seen in FIG. 4, valve 44 includes also an outlet port 4 47,which communicates with the air springs, and a vent port 48 fordischarging bleed air to the atmosphere. Customarily the ports 48 of allvalves in a single installation are connected together through suitableplastic or metal tubing, so as to have a common discharge point. Thevalve 44 has a centrally bored passage 49 extending from the top to thebottom of the valve, with different-diameter portions that form chamberscommunicating with the respective ports 45, 47 and-48 as will appear. Aninlet chamber 51 is formed by an enlargement of the passage 49, beingclosed off at the bottom by a suitable base plate 52, which extendsacross and seals the base of the valve 44. The inlet chamber 51communicates directly with the inlet lport 45 and hence normallycontains air at high pressure,

which under static conditions therefore equals the pressure of thesource. A valve disc 53 normally seals off the top of the chamber 51,being urged against a valve seat 55 by a compresthat moderate pressureapplied downwardly against the disc 57 causes it to unseat withoutdisturbing the disc 53. The latter however will in turn be unseated ifthe downward motion of the disc 57 continues beyond a predeterminedpoint, such as may be associated with sudden increasesin the load on theplatform, or during startup operations, at which times the high-pressureinlet chamber 51 communicates directly with the outlet port 47, andhigh-'pressure air or other fluid passes freely from the source to therespective inlet connections 37 of the air springs, until an equilibriumcondition is reached.

At other times during normal cycling periods, the pressure in theintermediate pressure chamber 56 is maintained at a constantincrementabove that at the outlet port 47 and independent of the inlepressure, through the use of a pressure regulator 6l preferablyincorporated within the valve body 44. The regulator valve 6l itself isof generally conventional design and incorporates a high-pressurechamber 62 communicating with inlet chamber 5l. A valve, preferablycomprising a hardened ball 63 is held against seat 64 by a compressionspring 65, assisted also by the relatively high-pressure in the chamber62 acting against the ball. The ball may be depressed to admithigh-pressure air as by la pin 66 responding to the motion of aconventional regulator diaphragm or piston 67 to which the pin isattached. The piston 67, shown with an O-ring 69 for hennetic seal,operates within a close-fitting cylinder 68 and the piston functions asa moving partition dividing the cylinder into a lower-pressure chamber7l above the piston, and a higher-pressure chamber 72 below the piston.A heavyduty regulator spring 73 bears downwardly against the piston 67with a force determined by the position of a regulating screw 74threaded into the regulator body and operable through a head 75 with theaid of a suitable adjusting tool. Altematively, the head may be shapedas a thumb wheel shown in broken lines, for ease of operation. A locknut76, or similar device which may include a finger lever 77 forquick-locking action, holds the screw 74 in adjusted position. Thelowerpressure chamber 7l communicates with the outlet port 47 throughduct 78, and thus imparts substantially the prevailing air springpressure to the piston 67, assisting spring 73 in exerting downwardpressure. ln an equilibrium condition, however, this pressure is notadequate to open valve 63 introducing new air to the mounts, until thesystem signals a change in the platform position, as will appear. v

A sensing device 79 of improved design, best seen in FIGS. l and 4,transmits positional data from the platform 14 to the air control valvein a manner to produce corrective action, and upon completion of thecorrective servo action, to erase the original signal. The sensor 79comprises a smooth cylindrical rod 8l that smoothly slides within upperand lower smalldiameter portions of the bored passage 49, andparticularly within a close-fitting plastic bushing 82, with goodlubricating properties, sealed within the passage 49. The lower end ofthe rod 8l rests freely upon the valve disc 57 but the rod is ofinsufficient -weight of itself to open the valve. The clearance betweenthe periphery of the rod, and the surrounding portions of the bushing 82are minimal, to reduce leakage, which may be even more closelycontrolled by employing a sealing ring 83, located within a necked-downzone or groove inthe rod. The ring 83 may be of circular cross section,and it may be of moderately deformable elastomeric material, typicallyusing tetrafluorethylene or a related product having a l'ow coefficientof friction. lt is fitted to the surrounding wall preferably with aslight interfering fit so as to provide a relatively smooth slidingaction for the rod 8l, with no significant leakage of air past the ring.With small translation of the rod 8l, the ring 83`may even tend to rollin its groove, reducing the frictional effects nomially associated withsliding rings.

A port 84 allows for the continuous bleeding of such a small amount ofair from'the system as leaks into a bore 88 between the bottom of thesensing rod 8l and the valve disc 57. The rate of flow is controlled bythe type of finish used on the ad- I joining surfaces, the type ofmaterials used o'n the mating sufficient only to provide a-gradualcontinuous reduction in the pressure exerted on the pistons 26 so thatafter a predetermined interval a resultant finite contraction in thevolume of the pressurized fluid within an air spring, contracts thediaphragm, producing a measurable lowering of the platform 14. Thisdeviation from an originally established .normal position may beinfinitesimal, that is, in microinches, but it is faithfully transmittedto the sensing rod 8l, in any convenient manner, but preferably througha small filamentary linkage that transmits axial forces, but lacksrigidity to exert significant lateral forces that might cause binding ofthe sensing rod. As an addedrprecaution to the buildup o f pressurewithin the intermediate-pressure chamber 56, as might occur if a foreignparticle blocks full seating of valve 63, a tiny bleed hole, 60typically made with a 07l drill, may extend through the disc 57, toconnect chamber 56 with the air springs. A similar result might beobtained by having a controlled degree of porosity at the joint betweenthe disc 57 and the seat 58, as by employing mating surfaces ofpredetermined roughness. The amount of leakage however is not of amagnitude to materially disturb the moderate differential pressurebetween the chamber 56 and the port 47. As shown in FIGS. 1 and 4, astraightenedwire 86, for example of hardened stainless steel or musicwire, extends from the sensing rod 8l to a bracket 87 secured beneaththe platform, Threaded stems 85 may be soldered or otherwise attached toone or both ends of the wire, and the assembly is adjustably secured byscrew threads to the sensing rod and bracket respectively, and heid inthe desired relationship to these parts as by locknuts 89.

Assuming that the platform l4 is in its normal position, the system willbe in equilibrium with the movable parts of the air spring 2l and of thevalve 44 and regulator 6l in the positions shown in FlGS. 2 and 4. lf anadditional load is applied to the platform, or if in the passage of atime interval the piston 26 retracts, the slight resulting incipientdownward motion of the platform applies a pressure to wire 86 openingvalve 57 by a suicient amount to cause a corrective flow of air from theintermediate-pressure chamber 56 through port 47 t0 the inletconnections 37, tending to restore the platform to its originalposition. `Simultaneously with the slight opening of valve 57, air fromthe intermediate-pressure chamber 56 also flows through port 78 andincreases the pressure within the lowerpressure chamber 71, helping toactuate valve 63 sufficiently to restore the predetermined pressure inthe intermediatepressure chamber 56. Similarly if the load on theplatform is lightened, the platform tends to rise on its air springsupports, and the incipient motion, transmitted through the relativelyvfine wire 86 lifts the-rod 8l from the disc S7, allowing free bleedingof air from the air springs via the outlet port 47 to the bore 88 andout through the vent 48.

A deviation of the platform has been found t occur, with correctiveservoaction, when less than one-tenth ounce of load change occurs on theplatform. The resulting deviation in milliinches or microinches often isnot discernible to the naked eye so that the motion might properly beconsidered as incipient motion. Obviously the motion is real and can bedetected -with suitable instruments. ln short, the regulator, by beingresponsive to the differential between the pressures of the mount and ofthe intermediate pressure chamber respectively, maintains the latterchamber at a reasonably constant pressure that nevertheless issubstantially independent ofthe actual mount pressure, and of themagnitude of the pressure of the air source, so that the devicefunctions properly over the full range of supply pressures. The softnessof the response of the system is an inverse function of the differentialpressure between the chamber 56 and that at the outlet port 47. Assuminga fixed setting of the bleed valve 42, the lower the pressure in chamber56 relative to port 47, the more softness, or delay in the correctiveaction, but the greater the sensitivity a constant differential inchamber 56, of say l0 or l5 p.s.i., as compared with an input pressureof some |00 psi. and a lt has been found desirable as a practical matterto maintain v' mount pressure of perhaps 70 to 8O p.s.i. Obviously theresponse ofthe system maybe varied by controlling the differentialpressure by adjustment of the regulator screw 74. For normal operatingconditions therefore the dynamic response of the system may be matchedto particular load or operating conditions merely by adjusting theconstant differential pressure by means of the regulator, and/orcontrolling the damping action by varying the amount of air bypassed tothe damping chamber.

At startup with the inlet 45 shut off from the supply, all air will havebeen bled from the system, the platform will be in its lowest position,and the rod 8l will have been depressed to an abnormal secondaryposition, well below its normal operating range. Consequently, valve 57will be fully open, and spring S6 compressed sufficiently to open valve53. Hence when highpressure air is admitted to chamber 51, the air flowsdirectly to port 47 through valves 53 and 57, bypassing regulator 6l,the intermediate chamber pressure and directly through to the airsprings 2l and damping chamber 43. This action appreciably reduces thestartup time, possibly by a matter of several minutes, and mayrepresent'more than a l0 -fold saving in startup time over currentlyknown equipment. A similar abnormal operating condition may arise when aheavy load is suddenly applied to the table, in which case a quickdownward responsive movement of the rod 8l to a secondary positionimparted by axial motion of the filament 86, opens both valves 56 and53, giving more immediate response by briefly connecting the air springsdirectly with the pressurized source, until equilibrium is reached.Since the filament 86 is relatively flexible any lateral motion at oneend of the wire relative to the other end results in a compliant motionof the wire without imparting significant lateral forces to the rod 8l.

Conversely when a load is removed from the platform, as when the load ishoisted by a crane, a sudden significant raising of the platform by theair springs logically ensues. The rod 8l hence is lifted by wire orfilament 86 allowing air to bleed through bore 88 and out of port 84 andvent 48. The port 84 may be of limited size, restricting the flowsomewhat, unless the load change is of such magnitude to cause rod 8l torise to a secondary upper position, wherein the O-ring 83 is clear ofthe bushing 82 and no longer seals the passage 49. The normal clearanceof even a few thousandths of an inch between rod 8l and the passage 49then provides a peripheral escape path whose cross section exceeds thatof port 84, and which contributes significantly to the bleeding of airfrom the air springs directly to exhaust chamber 91 and vent 48, therebymore quickly stabilizing of the platform. ln extreme cases, as when theplatform or the surface plate is lifted suddenly from its supports, therods 8l even have been forcibly ejected completely from their housingsby the force of the air in thc mount system, the wires 86 likely beingdeformed in the process if their upper ends are contained. The suddenejection of the sensory rods operates as a fuse or safety mechanism toprotect the air springs and other parts of the system by completelyventing the air springs to the atmosphere through the open passageway49.

Various connections between valves and air springs may be arranged,according to the required nature of support, and the degree of controlneeded. lf the need is simply to maintain f height at a given point, asingle valve and sensor may be used,

and a group of air springs connected in tandem to the single outlet port47. Since three points are needed to define a plane,

any system requiring orientation of a plane fequires at least threesensors and controls, with at least one neighboring air spring operatedby each. Likewise, if a pendulous platform needs control only as toheight, a single spring and valve is sufficient. With the systemillustrated, four separated air springs are used, each of two beingcontrolled by separate valves and sensors, and the remaining two beingoperated in tandem by the third valve and sensor.

We claim:

l. A self-leveling vibration-isolated mounting system comprising aplatform, pressure-responsive pneumatic means for adjustably supportingsaid platform, a sensor responsive to deviations in the position of saidplatform from a predetermined norm, and valve means operable by saidsensor for conducting pneumatic fluid from a pressurized source to saidpneumatic means, said valve means including an inlet port for connectionto said pressurized source of pneumatic fluid, an intermediate-pressurechamber for receiving pneumatic fluidv from said inlet port, an outletport for receiving pneumatic fluid from said intermediate pressurechamber, and pressure regulator means operative to maintain asubstantiallyconstant I differential between the pressure acting at saidoutlet portancl the pressure in said intennediate chamber.

2. A vibration-isolated mounting system as claimed in claim l, whereinsaid differential is maintained substantially independent ofthepressures at said ports.

3. The invention of claim 1, wherein said valve means includes a valvebody enclosing said regulator means.

4. The invention of claim l, wherein said regulator-means is operable tocontrol the flow of said fluid by' a predetermined moderate portion ofthe difference in the pressures between said inlet and outlet ports. v

5. A vibration-isolated mounting system as set forth in claim l, whereinsaid pressure-responsive pneumatic means supports said platfonn at apoint above the center of gravity of said platform, to render saidplatform pendulous.

6. A vibration-isolated mounting system as set forth in claim l, whereinsaid sensor includes a flexible filarnentary member extending betweensaid platform and said valve means, said member being sufficiently rigidas to transmit between said' platform and said valve means relativemotion axial of said tilamentary member while being complaint to motionof said platform transversely of said member.

7. A vibration-isolated mounting system as set forth in claim l, whereinthe response time of said pressure-regulator means exceeds the naturalperiod of said system.

8. A vibration-isolated mounting system as set forth in claim l,including a damping chamber also communicating with said valve means andwith said pneumatic means, and a throttle device for regulating theproportion of fluid flowing from said source to said pneumatic means andto said damping chamber respectively.

9. Apparatus as claimed in claim 7, wherein said damping chamber has avolumetric capacity substantially greater than the volumetric capacityof said pneumatic means.

l0. ln a stabilized structure having pneumatic positioning meansresponsive to controlled pressure of air for adjusting the position ofsaid structure, and a sense responsive to deviations in the position ofsaid structurefrom a predetermined normal position for regulating theflow of compressed air to said positioning means, the improvementcomprising an air control valve having an inlet chamber forcommunication with a supply of air under pressure, an outlet port forcommunicating with said pneumatic positioning means, anintermediatepressure chamber, a first-valve means actuated by saidsensor for conducting air from said intermediate-pressure chamber tosaid outlet port, and regulator valve means having pressureresponsivemeans communicating respectively with said outlet port and with saidintermediate-pressure chamber, and being operable by adifferentialpressure between said outlet port and said intermediate-pressure chamberfor controlling the passage of air from said inlet chamber to saidintermediatepressure chamber.

ll. Apparatus as claimed in claim l0, but including a second valve meansactuated by said sensor in response to an abnormal deviation in theposition of said structure from the predetermined normal position, saidsecondvalvel means then being operable to bypass said regulator valvemeansfand to 4connect said outlet port directly with said inlet chamber.

l2. Apparatus as claimed in claim l0, wherein said regulator valve meansincludes a movable member for controlling differential pressure that issubstantially independent of the magnitude of the supp ly pressure butnormally a relatively small part of the supply pressure. y 13. Apparatusas claimed in claim l0, wherein said regulator valve pressure-responsivemeans includesa lower-pressure l sure chamber, said partition beingurged by said spring means and by the pressure in said lower-pressurechamber in a direction to admit air from said inlet chamber, and beingurged by the pressure in said higher-pressure chamber to block the flowof air from said inlet chamber.

14. Apparatus as claimed in claim l0, including means for regulating theeffective force of said spring means.

l5. Apparatus as claimed in claim l0, including a bleed path extendingbetween said intennediate-pressure chamber and said outlet port, saidpath allowing continuous predetermined minimal flow of air to bypasssaid first-valve means to help in minimizing Athe differential pressurebetween said intermediate-pressure chamber and said outlet port.

16. A vibration-isolated mount, comprising a load-bearing platform, aplurality of air springs supporting said platform at spaced points, avalve for each of said air springs, sensing means associated with eachof said valves for controlling the flow from a source of air underpressure to said respective springs in response to deviations in theposition of said platform from an established norm, and regulator meansfor reducing the pressure from said source to a substantially con- Ystant increment above a normal pressure required in said air springs forthe support of said platform.

17. The method of supporting a stabilized structure within predeterminedlimits from an established normal position, comprising adjustablysupporting the structure pneumatically with fluid under normal pressure`detecting incipient deviations in the position of said structure fromsaid normal positions as during a reduction in said normal pressure,varying the pressure of said fluid applied to said structure inaccordance with said deviations so as to restore said normal position,and maintaining the upper limit 'of said applied fluid pressure at anestablished increment above said normal pressure.

18. ln a self-leveling platform having pneumatic supporting andpositioning means responsive to controlled pressure of air for adjustingthe level of said platform, and a sensor responsive to deviations in theposition of said platform from a predetermined normal position forregulating the flow of compressed airito said positioning means, theimprovement comprising an air control valve having an inlet chamber forcommunication with a supply of air under pressure, an outlet port forcommunicating with said pneumatic positioning means, and vent means,said sensor including means operable when said sensor is moved in onedirection from anormal position to admit compressed air to said outletport, and being operable when in a normal position to bleed smallpredetermined quantities of leakage air from said outlet port toI saidvent means, said sensor also including means when said sensor is movedin the opposite direction to provide paths of successively increasedcross section and accordingly of progressively reduced resistance to theflow of air from said outlet port to said vent means as the motion ofsaid sensor increases.

19. Apparatus as claimed in claim 18, wherein said sensor includes a rodnormally responsive to the motion of said platform and being slidablycontained within a close-fitting bore within said valve, said rod beingsufficiently responsive to the air pressure at said outlet port whensaid platform moves beyond predetermined limits as to be ejected fromsaid bore, whereupon said bore provides an additional path for ventingair from said outlet port.

` "sense" I "positions" should read position UNITED STATES PATENT OFFICECERTIFICATE 0F CORRECTION May ll, 1971 3,578,278 Dated Patent No.

` NormanC. Pickering et al.

Inventor(s) lt is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

line `75, "ports" should read parts Column 8 line 48 Column 5, Column 6,line l5, "O71" should read #7l Column l0, lines l and 2,

should read sensor Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR.Attesting Officer UscoMM-Dc enen-psg/f;

U S` GOVERNMENT PRINTING OFFICE: i902 0-366-3v FORM PO-1050 [1C-69)

1. A self-leveling vibration-isolated mounting system comprising a platform, pressure-responsive pneumatic means for adjustably supporting said platform, a sensor responsive to deviations in the position of said platform from a predetermined norm, and valve means operable by said sensor for conducting pneumatic fluid from a pressurized source to said pneumatic means, said valve means including an inlet port for connection to said pressurized source of pneumatic fluid, an intermediate-pressure chamber for receiving pneumatic fluid from said inlet port, an outlet port for receiving pneumatic fluid from said intermediate pressure chamber, and pressure regulator means operative to maintain a substantIally constant differential between the pressure acting at said outlet port and the pressure in said intermediate chamber.
 2. A vibration-isolated mounting system as claimed in claim 1, wherein said differential is maintained substantially independent of the pressures at said ports.
 3. The invention of claim 1, wherein said valve means includes a valve body enclosing said regulator means.
 4. The invention of claim 1, wherein said regulator means is operable to control the flow of said fluid by a predetermined moderate portion of the difference in the pressures between said inlet and outlet ports.
 5. A vibration-isolated mounting system as set forth in claim 1, wherein said pressure-responsive pneumatic means supports said platform at a point above the center of gravity of said platform, to render said platform pendulous.
 6. A vibration-isolated mounting system as set forth in claim 1, wherein said sensor includes a flexible filamentary member extending between said platform and said valve means, said member being sufficiently rigid as to transmit between said platform and said valve means relative motion axial of said filamentary member while being complaint to motion of said platform transversely of said member.
 7. A vibration-isolated mounting system as set forth in claim 1, wherein the response time of said pressure-regulator means exceeds the natural period of said system.
 8. A vibration-isolated mounting system as set forth in claim 1, including a damping chamber also communicating with said valve means and with said pneumatic means, and a throttle device for regulating the proportion of fluid flowing from said source to said pneumatic means and to said damping chamber respectively.
 9. Apparatus as claimed in claim 7, wherein said damping chamber has a volumetric capacity substantially greater than the volumetric capacity of said pneumatic means.
 10. In a stabilized structure having pneumatic positioning means responsive to controlled pressure of air for adjusting the position of said structure, and a sense responsive to deviations in the position of said structure from a predetermined normal position for regulating the flow of compressed air to said positioning means, the improvement comprising an air control valve having an inlet chamber for communication with a supply of air under pressure, an outlet port for communicating with said pneumatic positioning means, an intermediate-pressure chamber, a first-valve means actuated by said sensor for conducting air from said intermediate-pressure chamber to said outlet port, and regulator valve means having pressure-responsive means communicating respectively with said outlet port and with said intermediate-pressure chamber, and being operable by a differential pressure between said outlet port and said intermediate-pressure chamber for controlling the passage of air from said inlet chamber to said intermediate-pressure chamber.
 11. Apparatus as claimed in claim 10, but including a second valve means actuated by said sensor in response to an abnormal deviation in the position of said structure from the predetermined normal position, said second valve means then being operable to bypass said regulator valve means, and to connect said outlet port directly with said inlet chamber.
 12. Apparatus as claimed in claim 10, wherein said regulator valve means includes a movable member for controlling the flow of air from the supply of air under pressure to said intermediate chamber, in response to a substantially constant differential pressure that is substantially independent of the magnitude of the supply pressure but normally a relatively small part of the supply pressure.
 13. Apparatus as claimed in claim 10, wherein said regulator valve pressure-responsive means includes a lower-pressure chamber communicating with said pneumatic means, spring means, a higher-pressure chamber communicating with said intermediate-pressure chamber, and a movable partition separating said lower-pressure chamber from said hIgher-pressure chamber, said partition being urged by said spring means and by the pressure in said lower-pressure chamber in a direction to admit air from said inlet chamber, and being urged by the pressure in said higher-pressure chamber to block the flow of air from said inlet chamber.
 14. Apparatus as claimed in claim 10, including means for regulating the effective force of said spring means.
 15. Apparatus as claimed in claim 10, including a bleed path extending between said intermediate-pressure chamber and said outlet port, said path allowing continuous predetermined minimal flow of air to bypass said first-valve means to help in minimizing the differential pressure between said intermediate-pressure chamber and said outlet port.
 16. A vibration-isolated mount, comprising a load-bearing platform, a plurality of air springs supporting said platform at spaced points, a valve for each of said air springs, sensing means associated with each of said valves for controlling the flow from a source of air under pressure to said respective springs in response to deviations in the position of said platform from an established norm, and regulator means for reducing the pressure from said source to a substantially constant increment above a normal pressure required in said air springs for the support of said platform.
 17. The method of supporting a stabilized structure within predetermined limits from an established normal position, comprising adjustably supporting the structure pneumatically with fluid under normal pressure, detecting incipient deviations in the position of said structure from said normal positions as during a reduction in said normal pressure, varying the pressure of said fluid applied to said structure in accordance with said deviations so as to restore said normal position, and maintaining the upper limit of said applied fluid pressure at an established increment above said normal pressure.
 18. In a self-leveling platform having pneumatic supporting and positioning means responsive to controlled pressure of air for adjusting the level of said platform, and a sensor responsive to deviations in the position of said platform from a predetermined normal position for regulating the flow of compressed air to said positioning means, the improvement comprising an air control valve having an inlet chamber for communication with a supply of air under pressure, an outlet port for communicating with said pneumatic positioning means, and vent means, said sensor including means operable when said sensor is moved in one direction from a normal position to admit compressed air to said outlet port, and being operable when in a normal position to bleed small predetermined quantities of leakage air from said outlet port to said vent means, said sensor also including means when said sensor is moved in the opposite direction to provide paths of successively increased cross section and accordingly of progressively reduced resistance to the flow of air from said outlet port to said vent means as the motion of said sensor increases.
 19. Apparatus as claimed in claim 18, wherein said sensor includes a rod normally responsive to the motion of said platform and being slidably contained within a close-fitting bore within said valve, said rod being sufficiently responsive to the air pressure at said outlet port when said platform moves beyond predetermined limits as to be ejected from said bore, whereupon said bore provides an additional path for venting air from said outlet port. 